<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <span>名：</span><input type="text" v-model="firstName"> <br>
        <span>姓：</span><input type="text" v-model="lastName">
        <div>{{fullName}}</div>
    </div>
    
    <script src="../node_modules/vue/dist/vue.min.js"></script>
    <script>
        var vm =new Vue({
            el:'#app',
            data:{
                firstName:'',
                lastName:'',
                fullName:''
            },
            methods: {
                
            },
            watch:{
                firstName:function(val){
                    this.fullName = val + ' ' + this.lastName;
                },
                lastName:function(val){
                    this.fullName = this.firstName + ' ' + val;
                }
            },
            computed:{
                fullName:function(){
                    return this.firstName + ' ' + this.lastName;
                }
            }
        })
    </script>
</body>
</html>